1. Field of the Invention
The invention concerns a spacing profile for a spacing frame, which is to be fitted in the edge area of a double-glazing unit, forming an interspace, with a profile body of a plastic material possessing low thermal conductivity and with a diffusion-impermeable metal foil which is bonded to the profile body so as to establish a material fit.
In particular, the invention relates to spacing profiles of the aforementioned type where the profile body incorporates contact flanges for contact with the insides of the panes of the double-glazing unit and a connecting flange bridging the interspace in installed state, by means of which at least two contact flanges are connected to one another, where the spacing profile additionally comprises a desiccant cavity arranged between the contact flanges and a metal foil which extends essentially over the entire width of the spacing profile, where the metal foil is bonded to establish a material fit to cavity-side surfaces of the contact flanges, as well as to adjacent end sections connecting flange.
The profile body made of plastic material which possesses low thermal conductivity represents the principle part of the spacing profile in respect of volume and imparts its cross-sectional profile to it.
Within the scope of the invention, the panes of the double-glazing unit are normally glass panes of inorganic or organic glass, without the invention being restricted thereto. The panes can be coated or otherwise finished in order to impart special functions to the double-glazing unit, such as increased thermal insulation or sound insulation.
2. Description of the Prior Art
For a considerable time, instead of metal spacing profiles, plastic spacing profiles have been used in order to take advantage of the low thermal conduction of these materials. By materials with low thermal conductivity are generally meant those which possess a coefficient of thermal conductivity which is significantly lower than that of metals, that is to say at least by a factor of 10. The coefficients of thermal conductivity X are typically of the order of 5 W/(m*K) and less; preferably, they are lower than 1 W/(m*K) and more preferably lower than 0.3 W/(m*K).
Of course, plastics generally possess low impermeability to diffusion in comparison with metals. In the case of plastic spacing profiles, it is therefore necessary to ensure by special means that atmospheric humidity present in the environment does not penetrate into the interspace to the extent that the absorption capacity of the desiccant generally accommodated in the spacing profiles is not soon exhausted, thus impairing the reliability performance of the double-glazing unit. Furthermore, a spacing profile must also prevent filler gases from the interspace, such as for example argon, krypton, xenon, sulphur hexafluoride, escaping from it. Conversely, nitrogen, oxygen etc., present in the ambient air may not enter the interspace. Where impermeability to diffusion is involved below, this means impermeability to vapor diffusion, as well as impermeability to gas diffusion for the gases stated.
To improve the impermeability to vapor diffusion, DE 33 02 659 A1 suggests to provide a plastic spacing profile with a vapor barrier by fitting a thin metal foil or a metallized plastic film on the plastic profile on the surface which faces away from the interspace in the installed state. This metal foil must fully span the interspace so that the desired vapor barrier effect occurs.
Nowadays, it is preferred to produce one-piece spacing frames from spacing profiles which are bent at three or four corners and for which joining of the end sections is effective by means of corner connectors inserted in the end sections or a straight connector. Here, an endeavor is made to carry out the corner bending as simply as possible in production, in particular without expensive prior heating.
In order to permit cold-bending of spacing profiles made of materials with low thermal conductivity, spacing profiles have been developed, where the profile body of material with low thermal conductivity and being elastically-plastically deformable is bonded to a plastically deformable reinforcing layer, preferably a metal layer, so as to establish a material fit. This reinforcing layer can also be impermeable to diffusion and span the entire width of the interspace, as a result of which the necessary impermeability to diffusion of the spacing profile is achieved. Such a spacing profile has been introduced under the name THERMOPLUS.RTM. TIS for example in the brochure "Impulse fur die Zukunft (Impulses for the Future)" of Flachglas AG, Germany, and is described in the utility model DE 298 14 768 U1, which has an earlier priority date than the present patent application. In a preferred embodiment of this spacing profile, a polypropylene homopolymer having a Young's modulus of elasticity (modulus of elasticity) of 1,900 N/mm.sup.2 is used, whereas the reinforcing layer is fabricated from sheet iron having a thickness of less than 0.2 mm or from stainless steel having a thickness of less than 0.1 mm.
Spacing profiles consisting of a plastics-metal-foil sandwich generally have proved in practice. Though, there is still the problem that the cold-bendability, in particular in the area of the desiccant cavity, is limited. As the desiccant cavity is relatively rigid by virtue of its closed structure reinforced on three sides, this area can only be cold-bent with difficulty. Thus, it is of course thoroughly desirable for the contact flanges, that they should, on account of the sandwich construction of elastically-plastically deformable profile body material and plastically deformable (metal) reinforcing layer, possess a high degree of rigidity, so that the contact flanges should present a flat contact surface, even after cold-bending. In the case of the desiccant cavity, a high level of rigidity has however been found disadvantageous. Above all, the side walls of the desiccant cavity impart to the profile, in accordance with the state of the art, a comparably high moment of resistance to bending so that, during the cold-bending process, uncontrolled bulging of the side walls towards the contact flanges or undesirable deformation of the connecting flange can occur.
In single cases, it had also been observed that in particular at high bending speeds high level deformation forces occurred at some regions, so that the material fit between profile body and metal foil could not be maintained, whereupon the metal foil peeled off the profile body at some regions and showed cracking there. In particular, the free ends of the contact flanges of a profile according to DE 298 14 768 U1 are at risk, where the metal foil experiences a high deformation stress even during manufacture of the spacing profile. The uncontrolled foil separation and tears lead to impairment of the vapor-barrier effect and to mechanical instability of the profiles.